Tremolo arrangement for an electronic musical instrument employing feedback of modulated signal to modulator input

ABSTRACT

A carrier wave having a sub-audible frequency is modulated in amplitude by a modulating wave of a tone signal having an audible frequency, thereby producing a resultant modulated output signal including side band components deviated from the original tone signal frequency by a deviation amount equal to the carrier frequency. The frequency of the carrier wave is selected to be much lower than that of the modulating wave. The frequencydeviated signal thus obtained is fed back and admixed with the modulating wave to obtain a multiplicity of frequency-deviated signals. These signals are mixed with the original tone signal to produce an intricate tremolo effect.

OSCILLATOR United States Patent 1 1 3,699,233

Suzuki [451 Oct. 17, 1972 [5 TREMOLO ARRANGEMENT FOR AN 3,267,197 8/1966 Hurvitz ....-..84/1 .24 ELECTRONIC MUSICAL INSTRUMENT 3,629,484 12/ 1971 Suzuki ..84/1 .25 EMPLOYING FEEDBACK o 2,221,188 11/1940 Hammond et a1. ..84/1 .25 MODULATED SIGNAL o 2,322,884 6/1943 Roetken ..179/1 MODULATOR INPUT OTHER PUBLICATIONS [721 Invenm Symlchi Suzuki "amamatswlapan c. L. Alley and K. w. Atwood, Electronic Engineer- [73] Assignee; Nippon Gakki Seim Kabushiki ing, Second Edition, Copyright 1966 by John Wiley &

Kaisha Hamamatswshi Japan Sons, Inc. New York pp. 528 and 529.

[ Filedi J 1971 Primary Examiner-E. A. Goldberg 2 A L N 104,229 Assistant Examiner-Stanley J. Witkowski 1 pp 0 Attorney-Holman & Stern [30] Foreign Application Priority Data [57] ABSTRACT Jan. 12, 1970 Japan ..45/3343 A carrier wave having a sub-audible frequency is Jan. 23, 1970 Japan ..45/6523 modulated in amplitude by a modulating wave of a tone signal having an audible frequency, thereby [52] U.S. Cl. ..84/l.22, 84/ 1.24, 84/125, pr du g a r sultant modulated utput signal includ- 84/ 1 10 lng side band components deviated from the original 51] Int. Cl. ..G10h 1/04 tone signal frequency by a deviation amount equal to [58] Field of Search ..84/1.01, 124,125,010. 10, the carrier frequency- The frequency of the carrier 84/122. 331/106. I79 J wave is selected to be much lower than that of the modulating wave. The frequency-deviated signal thus 56] References cued obtained is fed back and admixed with the modulating wave to obtain a multiplicity of frequency-deviated UNITED STATES PATENTS signals. These signals are mixed with the original tone signal to produce an intricate tremolo effect. 3,157,725 11/1964 Wayne ..84/l.24 3,263,019 7/1966 l-lurvitz ..84/1.24 4 Claims, 6 Drawing Figures PHASE SHIFTER RI Q MIAY hlUSlCAL A g 'fl AMPLIFIER GENERATING FEE CIRCUIT D BACK AMPLIFIER R2 EXTREMELY LOW MODULATOR FUER,

FREQUENCY PATENTEDUCI I1 I972 SHEEI 1 [IF 2 Fl G. l

R| MS ww AKLSP MUSIC L souNI FBA \A SIGNAL AMPLIFIER EEJI T PS 3HA5E FEED BACK SH'FTER AMPLIFIER LFO M F EXTRE/MJELY Low M ouLAToR R2 F l G. 2

PHASE SHIFTER RI I K vv [G\ S asFII SP A FBA FEED-BACK CIRCUIT MPLIFIER LFO M F EXTREMELY Low MoIJuLAToR R2 FREQUENCY HLTER oscILLAToR Fl G. 5

. RI [q MS FILTER SP MusIcAL (A S gmu FT F2 A PLIFIER GENERATING PS #PHASE FEED-BACK CIRCUIT SHlFTER AMPLIFIER LFO M FI K I I R2 EXTREMELY Low 1 FREQUENCY MODULATOR FILTER OSCILLATOR PATENTEDnm n ma 3,699,233

SHEET 2 [IF 2 FIG. 3

* v f Affii Xf f 2Af J r 3 i m ||1:::|:: ammw i T illli UHF? f FREQUENCY (Hz) F l G. 4

0o FREQUENCWHZ) m 90 g -l80 m -27o 2 o I -36O LL 3 FIG. 6

LEVEL (dB) FREQUENCY (Hz) TREMOLO ARRANGEMENT FOR AN ELECTRONIC MUSICAL INSTRUMENT EMPLOYING FEEDBACK OF MODULATED SIGNAL TO MODULATOR INPUT BACKGROUND OF THE INVENTION This invention relates generally to tremolo effect producing devices, and more particularly to a type of device for creating tremolo effect sounds in a purely electrical manner.

Heretofore, there have been used tremolo or chorus producing devices wherein an electrical musical sound signal (as a carrier wave) is amplitude-modulated with a signal (as a modulating wave) having a desired frequency and wave form, or the electrical signal is converted into a sound signal through a loudspeaker rotating at a desired speed. (Hereinafter as far as an electronic musical instrument is concerned, a tremolo effect represents a modulation by a frequency ranging from 5 to Hz, while a chorus effect represents a modulation by a frequency ranging from 0.5 to 2 Hz.) However, in the first mentioned system, since only the amplitude modulation is employed, a frequency of the musical sound signal remains unchanged, and therefore the resultant sound is rather monotonous and the sound effect is very poor. On the other hand, in the second system, a Doppler effect is produced in the musical sound signal by the rotation of the loudspeaker, and as a result, the frequency and phase of the musical sound signal are varied, and the signal level is also varied with the variation of directivity whereby a wide spread sensation can be obtained. Therefore, the second system is very effective, but involves disadvantages such as excessively complicated rotating mechanism and driving mechanism of the loudspeaker and high production cost thereof. Furthermore there are possibilities of various undesirable noises such as wind noise and other mechanical noises being introduced at the time of rotation of the loudspeaker.

SUMMARY OF THE INVENTION It is accordingly a main object of the present invention to provide a novel organization of a tremolo or chorus effect producing device wherein all of the above-described drawbacks of conventional devices can be eliminated.

Another object of the present invention is to provide a tremolo effect producing device in which a tremolo effect which is very effective and rich in providing natural sound sensation can be obtained in a purely electronic manner.

A further object of the present invention is to provide a novel tremolo or chorus effect producing device which can operate in a purely electronic manner and is simple in construction and economical in production.

A still further object of the present invention is to provide a tremolo effect producing device, wherein the effect of a frequency deviation rate is averaged at every compass, and an outstanding tremolo effect is produced in the signal of string instruments, the signal of which is very rich in higher harmonics.

The nature, utility and the principle of the invention will be more clearly understood from the following detailed description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawings:

FIG. 1 is a block diagram illustrating an embodiment of the tremolo effect producing device according to the present invention;

FIG. 2 is a block diagram showing another embodiment of the tremolo effect producing device according to the present invention;

FIG. 3 is a chart of frequency vs. level of a signal obtained in the tremolo effect producing device according to the present invention;

FIG. 4 is a chart illustrating an example of the phase characteristic of a phase shifter employed in the tremolo effect producing device according to the present invention;

FIG. 5 is a block diagram of a further embodiment of the tremolo effect producing device according to the present invention; and

FIG. 6 exhibits a frequency spectrum of the musical sound signal obtained in the tremolo effect producing device shown in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION With reference now to FIG. 1, reference symbol MS represents a musical sound signal generating circuit which includes tone generators, tone keyers, tone coloring filters, tone color controls, and the like in case of, for instance, an electronic organ, and a phase shifter PS is adapted to shift the phase of a musical sound signal by a phase amount in response to its frequency and, if required, to obtain its phase shifting characteristic as shown in FIG. 4.

An extremely low frequency oscillator LFO generates an extremely low (subaudible) frequency signal the frequency (0.5 to 10 Hz) of which is substantially lower than the musical sound signal. A modulator M is adapted to amplitude-modulate the extremely low frequency signal (as a carrier wave) with the musical sound signal (as a modulating wave). A high-pass filter F serves to obtain only side hand signals by eliminating only the extremely low frequency signal out of a modulated output signal of the modulator M. Resistors R1 and R2 are employed for composing a mixer which mixes the original musical sound signal and the side band signals. An amplifier A amplifies the thus mixed signal. Reference symbol SP designates a loud-speaker. In the case where a balanced modulator is used as a modulator, no extremely low frequency component is included in the modulated output signal, and therefore it is not necessary to employ the high-pass filter F. A feedback amplifier FBA serves to feed back the side bank signals to the input side of the phase shifter PS or to the modulating terminal of the modulator M.

The phase shifter PS adapted to shift the phase of a musical sound signal by a shifting amount in response to its frequency gives a certain phase difference between an extremely low frequency signal (as a carrier wave to be modulated) furnished from the extremely low frequency oscillator LPG and the musical sound signal (as a modulating wave) so that an amplitude modulation and/or a frequency modulation can be obtained, thereby to attain a more intricate sound effect, but it is not necessarily required.

Hereinafter, a case wherein the phase shifter is not provided and the musical sound signal is directly applied to the modulating terminal of the modulator M, is described for convenience in exposition.

It is assumed that the musical sound signal is represented by a cosw t (w 2-n'f, f frequency the musical signal usually comprises a plurality of frequency components thus constituting a frequency spectrum band and the frequency thereof is varied in accordance with the progression of the musical performance, but for convenience in explanation in this specification, the musical signal is represented by only a single frequency of f Hz.), and the extremely low frequency signal is represented by a formula A cos Amt (Aw= 21rAf, Af= frequency), a both side band signal represented by the following formula can be obtained when the extremely low frequency signal (as a carrier wave) is amplitudemodulated with the musical sound signal (as a modulating signal) and the extremely low frequency component contained in the modulation output signal thus obtained is removed by utilizing the high-pass filter F:

mA/2 {cos Am) t+ cos (0) -Am)t} where m ha and m means the amplitude modulation factor (k is the modulation sensitivity). This signal is mixed with the original musical sound signal in the mixing circuit comprising the resistors R1 and R2, and as a result of which a signal represented by the following formula is obtained:

where a, and b, represent respective amplitudes, and a phase shift due to the filter is neglected.

On the other hand, a part of the output signal of the filter F is applied to the input side of the phase shifter PS after having been adjusted in phase and level through the feedback amplifier FBA. This signal amplitude-modulates the extremely low frequency signal in the modulator M in the same way as described above. Accordingly, the signal from the filter is represented by the following formula:

where b represents the amplitude, and a phase shift due to the feedback is neglected. Therefore, the formula of a mixed signal obtained by mixing with the original musical sound signal in the mixer will be as follows:

Thus, both of the upper and lower side hand signals are fed back to the modulating terminal of the modulator M, and as a result the mixed signal is represented by the following formula:

Zn a, cos 0) t+ b, cos (0) +iAw) t+ cos ((0 iAw) t}.i=l

The frequency spectrum of this signal is as shown in FIG. 3, in which frequencies are distributed at an interval of the extremely low frequency Af on both sides of the musical sound frequency f. Therefore, when this signal is properly amplified and then converted into sound through the loud-speaker, a tremolo effect sound whose frequency varies by frequencies of Af, 2Af through nAf can be obtained.

Moreover, the signal is equivalent to a signal containing many frequenciesflfiAflfi 2Af ..f:t: nAf, and therefore can be considered as a multi-rank sound source and the signal produces an outstandingly rich sound.

Thus, an example in which a bilateral band modula tion circuit comprising the modulator M, the extremely low frequency oscillator LFO and the high-pass filter F has been described. However, a single side band modulation circuit wherein a single side band signal is obtained higher or lower by as much as Af than the frequency of the musical sound signal, can be employed. In this case, it goes without saying that the output signal occupies either the right or left side of the frequency spectrum shown in FIG. 3.

In addition, the signal mixer may be provided with variable resistors instead of the resistor R, and R so that the mixing level can be adjusted as desired, or the mixer can be designed so that the signal mixing can be accomplished by an RC network at a proper phase relationship.

Another embodiment of the present invention is shown in FIG. 2 wherein the phase shifter PS is directly inserted in the musical sound signal path instead of being connected in the signal path to the modulator. However, this embodiment is substantially the same in function and effect as the example described with reference to FIG. 1.

A further example according to the present invention is illustrated in FIG. 5. This example is the same as that shown in ,FIG. 1 with the exception that a filter F, is used in place of the filter F shown in FIG. I, and an additional high-pass filter F, is provided on the output side of the feedback amplifier FBA. The filter F, is a high-pass filter which serves to obtain a single side band signal only by removing the extremely low frequency component from the modulated output signal of the modulator M, and likewise F, is a high-pass filter.

In the same manner as in FIG. 1, both the upper and lower side band signals are feed back, and as a result the mixed signal can be represented by the following general formula:

(I n practice, the phase of each side band signal is The resultant combination output signal thus obtained by feedback is of a composition having many side band signals spreading on both sides of the musical sound signal and contributes to producing a tremolo effect sound richer than that obtained without feedback. However, since the carrier signal (to be modulated), namely, the extremely low frequency Af from the extremely low frequency oscillator LFO is constant, the relative frequency deviation Af/f decreases with the increases with the increases with the increase of the musical sound signal frequency. Accordingly, the higher in compass a signal is, the more is the decrease of the tremolo effect thereof. In order to overcome this disadvantage, the abovementioned third embodiment of the present invention is so designed as to relatively increase the higher frequency component included in the side band signal by inserting the high-pass filter F in the feedback device. Thus, as shown with a frequency spectrum in FIG. 6, the spectrum in higher frequency is widened and the effect of the frequency deviation rate is averaged at every compass, whereby the tremolo effect is particularly improved in the signals of string instruments, which signals have a number of higher harmonics.

The example described above employs a bilateral band modulation circuit comprising the modulator M, an extremely low frequency oscillator LFO and a filter F However, it is capable of utilizing a single side band modulation circuit for obtaining a single side band signal either higher or lower by a frequency Af than the musical sound signal frequency. In this case, the frequency spectra of the output signals occupy only the right or left side of frequency 100 Hz, 500 Hz, and 5 kHz respectively, but, of course, almost the same effect can be obtained as described above.

While a few embodiments of the present invention have been illustrated and described in detail, it is particularly understood that the invention is not limited thereto or thereby.

I claim:

1. In a electronic musical instrument, a tremolo effect producing circuit comprising in combination: a musical sound signal generating circuit; a low frequency oscillator generating a low frequency signal of frequency substantially less than audio frequency range; an amplitude modulator having an input connected to said oscillator for receiving said low frequency signal as a carrier wave, and with a second input connected to said musical sound signal generating circuit for receiving said musical sound signal as a modulating wave, said modulator giving out a modulated output signal including side band signals and the carrier wave; a high-pass filter connected to an output side of said amplitude modulator for receiving said modulated output signal to eliminate said carrier wave and pass side band signals; a feedback amplifier connected between the output of said high-pass filter and said amplitude modulator for feeding back said side band signals as modulating waves; and mixer means conv nected to said musical sound signal generating circuit 

1. In an electronic musical instrument, a tremolo effect producing circuit comprising in combination: a musical sound signal generating circuit; a low frequency oscillator generating a low frequency signal of frequency substantially less than audio frequency range; an amplitude modulator having an input connected to said oscillator for receiving said low frequency signal as a carrier wave, and with a second input connected to said musical sound signal generating circuit for receiving said musical sound signal as a modulating wave, said modulator giving out a modulated output signal including side band signals and the carrier wave; a high-pass filter connected to an output side of said amplitude modulator for receiving said modulated output signal to eliminate said carrier wave and pass side band signals; a feedback amplifier connected between the output of said highpass filter and said amplitude modulator for feeding back said side band signals as modulating waves; and mixer means connected to said musical sound signal generating circuit and said highpass filter thereby to mix said musical sound signal and an output from the high-pass filter to produce a resultant output wave containing a tremolo effect.
 2. A tremolo effect producing circuit as claimed in claim 1, which further comprises a second high-pass filter connected between said feedback amplifier and said amplitude modulator.
 3. A tremolo effect producing circuit as claimed in claim 1, wherein said amplitude modulator is a single side band modulation circuit.
 4. A tremolo effect producing circuit as claimed in claim 1 wherein said mixer means comprises resistors. 